Sales of “natural” products within the personal care industry continue to show significant growth. Popular culture has driven this growth by popularizing the idea that there may be potential adverse effects to the body (toxicity) and to the environment (pollution, hastening of climate change, and environmental toxicity) associated with the use of ingredients derived from fossil fuels. The personal care industry has rapidly advanced its attempts to identify ingredients described as “renewable” and “sustainable,” that is, ingredients of non-fossil fuel origin for use in the formulation of virtually all cosmetic product types and forms.
In many instances, the industry has successfully identified replacements for many ingredients that are historically of fossil fuel origin. Examples of this are the replacement of mineral oils, silicones, and petrochemically-derived synthetic esters with vegetable oils and natural esters, synthetic fragrances with essential oils, and petrochemical preservatives with certain extracts.
Although used in marketing materials, the term “natural” has not yet been completely defined. However, efforts are underway by industry trade organizations to give the term a more concise and consistent meaning. Historically, it has been generally recognized that materials derived from renewable and/or sustainable, or otherwise non-fossil fuel sources are considered to be “natural” by the marketplace. More recently the definition of “natural” has been further refined. For example, there is a trend within the trade to prohibit animal-derived materials and plant-derived materials that are obtained from the use of genetically-modified organisms (GMO) from use in natural products.
Also, certain chemical processes used in the manufacture of ingredients, especially those processes that employ petrochemical solvents, generate unrecoverable waste, and/or consume excessive resources, are frowned upon or may otherwise be prohibited. The use of “Green Chemistry” principles in the production of cosmetic and personal care ingredients is rapidly becoming a positive benefit that can be exploited in the marketing of products produced using those principles. Thus, the evolving definition of “natural” currently includes products that are not petrochemically derived. However, the other concepts discussed above (non-animal, non-GMO, Green Chemistry) may be taken into consideration when creating “natural” products, and to satisfy market demands.
One particular challenge facing formulators of natural products relates to the identification of suitable emulsifiers. An emulsifier is a type of surfactant typically used to keep emulsions (metastable mixtures of immiscible fluids) well dispersed. Emulsifiers typically have a hydrophobic (water-fearing) and a hydrophilic (water-loving) moiety. In an emulsion involving an oil and water, emulsifiers will surround the oil with their hydrophobic moiety oriented toward the oil, thus forming a protective layer so that the oil molecules cannot coalesce. This action helps keep the dispersed phase in small droplets (micelles) and preserves the emulsion. Emulsifiers may be anionic, nonionic, or cationic. A good emulsifier for use in a personal care product is one that will maintain consistent emulsion characteristics such as particle size, appearance, texture, and viscosity, substantially constant for as long a period as possible since by their very nature, all emulsions due to their metastable nature will eventually separate into their constituent oil soluble and water soluble components. Stability of the emulsion is highly desirable in most products, since among other advantages, this stability contributes to an extended shelf life of the product and the maintenance of its initial aesthetic properties over time.
Although the vast majority of emulsifiers currently used personal care products are wholly or partially petrochemically derived such as polyethylene glycol (PEG) derivatives and amine quaternaries, a limited number of known emulsifiers may meet the current definition of natural. However, presently available natural emulsifiers fall only within the classes of nonionic and anionic emulsifiers.
The natural nonionic emulsifiers are typically partial esters of long chain fatty acids with a polyol. Examples are long chain partial esters of sugars, of alkylglucosides, and of polyglycerols. Although these nonionic emulsifiers can be effective in building stable emulsions, they do little or nothing to provide any conditioning and/or aesthetic benefits to the hair or skin because they are not substantive to these substrates, which are negatively charged.
The natural anionic emulsifiers are typically the long chain fatty acid soaps of fatty acids and sulfuric acid esters (sulfates) of fatty alcohols. These tend to be drying to the skin and provide no aesthetic or conditioning benefits because, like the hair and skin, they are negatively charged and therefore tend to be repelled by these substrates.
Currently there are no known natural cationic emulsifiers. Many personal care applications require or are greatly improved by the use of cationic emulsifiers. Owing to the fact that typical cationic emulsifiers are built from a long chain (hydrophobic) alkyl group attached to a hydrophilic moiety, they act as emulsifiers much the same way as the nonionic and anionic emulsifiers previously described. However, in a cationic emulsifier, the hydrophilic portion of the molecule is positively charged. This cationic moiety will electrostatically bind to (be substantive to) negatively charged substrates such as the hair and skin. The hydrophobic moiety, which is nonionic, has no affinity for the substrate, and will orient away from the substrate creating a protective layer of fatty material that can provide enhanced sensory properties. The property of substantivity differentiates the cationic emulsifiers from anionic and/or nonionic emulsifiers. It is substantivity that facilitates the conditioning benefits of the end product. Therefore, in addition to being excellent emulsifiers, cationic emulsifiers also deliver the benefits of improving the aesthetics of formulations that include them, and allowing the formulation of personal care products that can condition, moisturize, and repair the skin, hair, or nails. Cationic emulsifiers, unlike anionic and nonionic materials are therefore multifunctional.
Cationic emulsifiers, when used in hair care applications such as cream conditioners, provide excellent conditioning benefits such as improvement in application aesthetics, creaminess and richness of the conditioner, and improvements in such application properties as softening, anti-static behavior, fly-away, wet combing, and dry combing. When cationic emulsifiers, are used in skin care preparations, they are known to provide what is known in the industry as a “dry, light, powdery” skin feel that is a distinct advantage in many skin care products. Exemplary traditional cationic emulsifiers include quaternized cationic emulsifiers such as cetrimonium chloride, behentrimonium chloride and distearyldimonium chloride, and amidoamines such as stearamidopropyl dimethylamine and behenamidopropyl dimethylamine.
All of the traditional cationic emulsifiers are petrochemically derived; therefore, all of these cationic emulsifiers are not considered to be natural and therefore cannot be used in the formulation of natural products. Accordingly, there is a need in the art for natural cationic emulsifiers that have performance and use characteristics and substantivity similar to the traditional cationic emulsifiers.